Am I using the correct liquid injection valve

[marc5180]

I'm working on an AHU with an evaporator that has 4 seperate interlaced circuits each with its own TEV.
Outside there are 4 seperate outdoor units each with their own compressor and condenser.
They are having a problem with low suction pressures and we have fitted a danfoss KVC15 capacity regulating valve from compressor discharge to the suction and also fitted a danfoss TXI2 de superheating valve.

The KVC valve works fine but the liquid injection valve (piped from the liquid line to the compressor suction) does nothing.
Theres no temp difference across the valve at all so it must be closed or the orrifice is too small but even then I would expect some temp difference across the valve.

Upon commissioning the temperature of the bulb which is on the suction line gets up to 50degrees with a Superheat of 45degC (too high I know but it wasn't left like this for long)

It wasn't me who specced the valve and I wasn't sure if the TXI2 was the correct valve until I read the literature from Danfoss online and came across page 8 below that says 'Ordering range and then temp range' and it lists it as +100 to +130C.....
What is this? Is this the bulb temp range?

http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/PDAV0A202.pdf

[marc5180]

I suspect it's the bulb temp range on the discharge side and if that's the case it's the wrong valve because we want to control the suction superheat with the liquid injection valve.

[frank]

Hi Marc

The TXI is the wrong valve for your application as you don't have a 2 stage compressor set up.

What is the capacity of each circuit?

[marc5180]

Hi Frank, I thought as much.....

The capacity of each compressor at design conditions is 36kw, I selected the No1 orrifice which was about 10% of the required duty, is this the right orifice?

Which valve is the correct one?

[install monkey]

out of interest is the ahu full fresh air or recirc?

[marc5180]

out of interest is the ahu full fresh air or recirc?

Full fresh air mate

[install monkey]

good answer- is cooling disabled if inlet air under 16deg?

Full fresh air mate

[marc5180]

No cooling is disabled at 10C but it's something were looking at getting changed. Why do u ask?

[install monkey]

usually ahu's have dx circuits and you have problems setting superheat as the varying load- fresh air being 10deg at night and upto 30deg when the yellow ball is in the sky- typically fresh air at 16 deg wouldnt req mechanical cooling as its classed as free cooling- but no doubt ur gonna throw a spanner in my thoery by telling me its an operating theatre :p

[marc5180]

but no doubt ur gonna throw a spanner in my thoery by telling me its an operating theatre :p

Haha, not an operating theatre but a data hall and the coils are used for dehum primarily :D

[install monkey]

normally only the bottom circuit should be dehum

[marc5180]

Not on this one, the circuits are interlaced.

[install monkey]

you have a habit of finding weird ahu's!!:p (last 1 was that air handlers with the check valves)

[marc5180]

Tell me about it!!!

This ones a bit of a nightmare because the system is grossly mismatched

[marc5180]

Can anyone recommend me which liquid injection (de superheater) valve I should be looking for.

I've had a quick look but I can only seem to find the TXI2 2 stage valves.

[Brian_UK]

Have a look at Sporlanonline and under literature go for 10 thermostatic expansion valves.

Have a read of document 10-207 which highlights their Y1037 liquid injection valves, installation doc is SD-168.

[install monkey]

http://astro.berkeley.edu/~plambeck/CARMAdocs/WaterChiller/TraneHotGasBypass.pdf
bit of info

[marc5180]

Have a look at Sporlanonline and under literature go for 10 thermostatic expansion valves.

Have a read of document 10-207 which highlights their Y1037 liquid injection valves, installation doc is SD-168.


Thanks Brian, I enquired about this yesterday but the lead time was another couple of weeks.

I've ended up going for a danfoss TZ2 that was off the shelf.

[marc5180]

Thanks for everyone's help

[Aik]

For capacity regulation I use KVC, but I get gas from receiver (top) to the suction line. The gas from receiver has about constant and not so high temperature.

[Peter_1]

If it's a constant problem, why not change the gas to a lower enthalpy gas? Like from R407c to R134a.
Is a VFD not an option because energetic seen, injection is a bad solution.

[Peter_1]

I should use the same valve as used for the injection of the liquid in the evaporator.
Think about the fact you will inject liquid in the suction.--> Suction accumulator.
Why not inject cold gas (upper part receiver) between TEV and distributor?

[marc5180]

If it's a constant problem, why not change the gas to a lower enthalpy gas? Like from R407c to R134a.
Is a VFD not an option because energetic seen, injection is a bad solution.

A VFD may well be an option, I've emailed copeland and I'm waiting to hear back as to the min/max speed that the compressor can be run at.
My only worry is the fact that the Evap/condensers aren't evenly matched and so I'm not sure a VFD would work correctly .

[marc5180]

I should use the same valve as used for the injection of the liquid in the evaporator.
Think about the fact you will inject liquid in the suction.--> Suction accumulator.
Why not inject cold gas (upper part receiver) between TEV and distributor?

There's no receiver on the this system.

I wanted to inject the hot gas to the Evap inlet between TEV and distributor but I was overruled!!

[Aik]

Why not inject cold gas (upper part receiver) between TEV and distributor?
In my opinion, better inject hot gas between TEV and distributor if you have one evaporator (smaller KVC size) or for fine adjustment you need CPCE + LG.
If you have two or more evaporators, it would be better to use cold gas and inject it from the top of receiver to the suction line (through the KVC).

[Peter_1]

We have systems running at 30 Hz. What do you mean with evaporator/condenser not evenly matched. The only thing the VFD will do is reduce swept volume, the TEV will try to maintain a stable SH and perhaps you can use a condenser control on the fans if HP should drop too much.
What gas is it running now and do they have always these problems since start-up?
With a dehumidifier, load can vary within wide margins if humidity fluctuates.

[marc5180]

I believe Copeland compressors can also be run down to 30hz. The system is less than 12 months old and is grossly mismatched and the condenser/compressor is oversized by as much as 50-75%.

Because of this we have encountered a few problems, one of them being the low condensing pressures.

The system is still running with R407c.